NEW YORK -- A state senator accused of slashing his girlfriend's face with broken glass during an argument has waived his right to a jury.

Hiram Monserrate has pleaded not guilty to second-degree assault in the Dec. 18 incident at his apartment. He faces loss of his Senate seat if convicted on the top charge.

The trial will be decided by Judge William Erlbaum of state Supreme Court in Queens instead of a 12-member jury. It is slated to start Sept. 21.

The 42-year-old senator maintains he tripped and that the incident was an accident.

Prosecutors say his girlfriend, Karla Giraldo, who's 30, at first said he broke the glass and slashed her intentionally. She later changed her story. The wound required 20 stitches around her left eye.